The objectives of the Biological Evaluation Core are to provide fundamental information on the nature of each of the new compounds synthesized. The procedure will allow for the identification of fundamental characteristics of each compound in the most efficient manner. Information which will be obtained for each compound includes the affinity of the compound at opioid eta, delta, kappa receptors in mouse brain homogenate. The affinity of these analogues will be measured using standard competition assays against reference radiolabelled ligands at each of these receptors types. The data from the binding assays will allow for the measurement of receptor selectivity in binding. The activity of these compounds will be determined using standard isolated bioassay tissues, including the guinea-pig isolated ileum (GPI, eta bioassay) and the mouse isolated vas deferens (MVD, delta bioassay). These assay tissues will be used to assess determined using dose-response curves in each of the bioassay tissues- these data will allow for the estimate of receptor selectivity (GPI/MVD ratio). If the compound is not active as an agonist, it will be tested in vitro as an antagonist against submaximal doses of reference compounds which have already been characterized in these assays. This will provide a complete prolife in vitro of each compound tested. Additionally, the agonist analogues will be screened following i.c.v. administration to mice in vivo using standard antinocipeptive tests such as the fail-flick test. If the analogue is an agonist in the bioassay, but does not procure antinociception in the tail-flick test following i.c.v. administration. Although dose-response studies will be emphasize for the central (i.e.,i.c.v or i.th) routes, only single doses will be used as a screen for systemic studies in the Biological Evaluation Core in order to reduce the quantity of analogue initially synthesized. Dose-response studies by systemic routes will be performed for interesting analogues in the individual projects. The data obtained in the Biological Evaluation Core will be essential for the appropriate design of new molecules by the Chemistry group and will allow the PI's to choose interesting molecules for further study in their individual assays.